1. Field of the Invention
This invention relates to a method of filtering of a dairy stream.
2. Discussion of the Background
Whey is a major by-product of cheese making, which, for environmental reasons, presents a difficult waste disposal problem. Whey is typically composed of about 5 wt. % lactose, 1 wt. % protein and about 0.5 wt. % salts, where the balance of the mixture is water. While the protein component can often be recovered by ultra-filtration, and accordingly used in food products, the lactose component, has heretofore been of little value.
One method of increasing the economic value of whey waste streams is to isolate sialyloligosaccharides from the waste stream. Anion exchange chromatography is effective for removing charged sialyloligosaccharide components from lactose. The presence of salts, especially citrate salts from acid addition, can greatly reduce the effectiveness of sialyloligosaccharide removal, such that it is conventional to remove salts from a whey waste stream in order to achieve effective recovery of sialyloligosaccharides.
Methods for removing sialyloligosaccharide fractions have been reported, but the extraction and ion exchange methods have not been entirely satisfactory from the stand point of throughput and purity.
Shimatani et al. U.S. Pat. No. 5,118,516 report the isolation of sialic acid-containing lactose, from whey, skim milk or a deproteinized solution by (a) electrodialysis, or (b) ion exchange by a cation-exchange resin and a strongly basic anion-exchange resin, or (c) a combination of electrodialysis and ion exchange by the cation-exchange resin and the strongly basic anion-exchange resin to desalt the permeate.
Shimatani et al. U.S. Pat. No. 5,270,462 report a process of manufacturing a composition containing a high concentration of sialic acids, by adjusting the pH of cheese whey to be acidic, contacting the whey with a cation exchanger, followed by concentrating and desalting the eluent.
J P Kokai 01-168,693 reports the preparation of a sialic acid composition, by subjecting milk, non-fat milk, buttermilk or whey to ultrafiltration, fractionating at 20,000 to 500,000 Daltons at a pH of 4.0 to 6.0, followed by a second ultrafiltration, fractionating at 1,000 to 10,000 Daltons at a pH of 6.0 to 8.0 under 0.2 to 2.0 MPa, to remove impurities such as lactose. The residual is spray dried or lyophilized.
J P Kokai 03-143,351 reports the recovery of oligosaccharide bonding type sialic acid from an alkali cleaning waste liquid of anion exchange resin formed at desalting of whey, by neutralization, ultrafiltration, reverse osmosis, desalting, absorption of the sialic acid onto a strong basic type anion exchange resin, followed by elution, desalting and drying.
J P Kokai 59-184,197 reports the manufacture of oligosaccharides attached to sialic acids, by desalting a sialyloligosaccharide-containing molasses, passing the desalted solution through an anion exchange column, neutralizing the eluate and desalting the eluate by electrophoresis.
Gregory et al. U.S. Pat. No. 5,707,678 reports a method of microfiltration of milk or colostral whey, in which after removal of fat and casein, ultrafiltration at a pH of from 4.5 to 5.0 provides for a whey product which can be microfiltered without fouling of a microfilter membrane or depth filter. The isolation of sialyloligosaccharides is not reported.
Marquardt et al. U.S. Pat. No. 4,497,836 reports a process for preparing a product suitable for use in infant food formulas in which a mineral rich edible cheese whey is subjected to ultrafiltration to produce a protein-rich retenate and a lactose-rich permeate. The lactose-rich permeate is then partially demineralized, such as by electrolysis and blended with the protein-rich retentate. In this fashion, demineralization is possible. Also in this process, the retentate is a protein-rich composition and the permeate is rich in lactose and minerals. The creation of a retentate rich in sialyloligosaccharides is not disclosed.
Venkatsubramanian et al. U.S. Pat. No. 4,376,023 reports a process in which a product stream comprising dextrose and oligosaccharides is separated in an electro-osmosis cell, by using alternating ion exchange membranes of high and low permeability, in which dextrose is selectively removed resulting in separate effluent streams enriched in dextrose and oligosaccharide respectively are obtained.
Hall U.S. Pat. No. 4,081,326 reports a method of obtaining an oligosaccharide composition, essentially free of G.sub.4 and lower saccharides, by treatment of an oligosaccharide composition containing G.sub.4 and lower saccharides with both a baker's yeast and a maltase.
Herrmann U.S. Pat. No. 4,844,923 reports a method of removing serum proteins from milk products by acidic precipitation, in which at least partial demineralization prior to acid precipitation was found to increase greatly the efficiency of the process. Removal of sialyloligosaccharides by reverse osmosis is not disclosed.
Eustache U.S. Pat. No. 4,042,576 reports a method of extracting glycoproteins and sialic acid from whey, in which proteins are flocculated by thermal treatment and the supernatent is then ultrafiltered. The ultrafiltration retentate is treated by hydrolysis, and the sialic acid is then extracted from the hydrolysis supernatent. Adjustment of the pH in the ultrafiltration to control the retentate composition is not disclosed.
Brian et al. U.S. Pat. No. 5,714,075 report processing of a cheese processing waste stream in which sialyloligosaccharides are obtained, by ion exchange chromatography to obtain the lithium salt of a sialyloligosaccharide and by extraction with a solvent.
A specific problem with purity encountered with isolation of sialyloligosaccharides by filtration methods, is separation from lactose. Due to similarities in molecular size, it is often difficult to isolate sialyloligosaccharides, in the absence of lactose, from a waste stream by filtration. Accordingly, filtration methods of obtaining sialyloligosaccharides in high purity, from a dairy stream would be welcome.
The present invention addresses this problem by providing a method of processing a dairy stream containing sialyloligosaccharides and lactose, in which the dairy stream is treated to effect hydrolysis of lactose prior to separation of sialyloligosaccharides.